1. Field of the Invention
The present invention relates to a measuring apparatus and a measuring method that are less subjected to influences of the noise, the spurious, etc. with a simple configuration when a phase delay characteristic between an input signal and an output signal of a measured device such as an optical communication component, or the like is measured.
2. Description of the Related Art
The conventional apparatus of this type for measuring the phase delay characteristic between the input signal and the output signal of the measured device such as the optical communication component, or the like, is described in the following.
FIGS. 4A and 4B are views for explaining the principle of the phase measuring portion to measure the phase delay characteristic in the prior art. FIG. 4A is a block diagram showing a configuration of a portion and FIG. 4B is a waveform diagram for explaining the principle of the portion.
In FIG. 4A, the ALC or the limiter amplifiers 41-1, 41-2 shape a reference signal (IF-R signal) and a signal that is passed through the tested device, i.e., a measured signal (IF-A/B signal) into pulse waveforms shown in FIG. 4B respectively to output the pulse signals. Then, the threshold detecting circuits 42-1, 42-2 detect rising time points of the reference signal (IF-R signal) and the measured signal (IF-A/B signal) respectively, and then provide them to the phase-difference comparing means (counter) to measure the phase difference between them.
In this phase-difference comparing means, the phase difference can be measured by counting the number of clocks between the leading edge of the reference signal (IF-R signal) and the leading edge of the measured signal (IF-A/B signal).
The principle of this apparatus is simple, but the signal purity of the oscillator that generates the reference signal, the characteristic of the employed parts, etc. affect the measurement error. Thus, the signal purity of the oscillator is very critical to implement the high-accuracy measurement.
Also, in order to time the phase difference with high accuracy, there is a problem that the clock signal of the extremely high frequency must be supplied to the counter.
FIG. 5 are views for explaining the principle of another phase measurement to measure the phase delay characteristic in the prior art.
In FIG. 5, the amplifiers 51-1, 51-2 provides the reference signal (IF-R signal) and the signal that is passed through the tested device, i.e., the measured signal (IF-A/B signal) to the synchronous detector 53 that detects the baseband I signal (in-phase component) and the baseband Q signal (quadrature component) as the detected outputs.
The baseband I signal (in-phase component) and the baseband Q signal (quadrature component) are output as the time-series data, and are output as phase difference time-series data based on the arc tan calculation in the phase-difference calculating circuit 54.
Then, the phase-difference signal given as the time series data are equalized by the equalization 55, and thus the phase-difference between the reference signal (IF-R signal) and the measured signal (IF-A/B signal) can be derived as the measured result.
In this case, as shown in an elliptic circle of FIG. 4, the calculation in the synchronous detector 53, the baseband I signal (in-phase component), is obtained by multiplying the reference signal (IF-R signal) and the measured signal (IF-A/B signal) by virtue of the multiplying circuit 531-1 and passing the resultant signal through the low-pass filter (LPF) 533-1.
Also, the baseband Q signal (quadrature component) is obtained by multiplying the signal, whose phase is shifted from the reference signal (IF-R signal) by 90 degrees by phase converter 532, and the measured signal (IF-A/B signal) by virtue of multiplying circuit 531-2 and passing the resultant signal through the low-pass filter (LPF) 533-2.
In this apparatus, it is possible to construct the apparatus by either the hardware or the software.
In the case where the apparatus is constructed by the software, the AD converter circuit and the sampling circuit are needed, and the phase difference can be measured with relatively high accuracy even if the sampling is carried out based on the low-speed clock. However, since the measured result is output as the time series data, such measured result is readily affected by the noise, and thus various measures are needed such that the LPF provided after the synchronous detection must be set to the narrower bandwidth, the measured results that are taken plural times must be averaged, or the like.
Then, these measures bring about an increase in the measuring time and also put a limit on the higher accuracy.
It is an object of the present invention to provide a measuring apparatus and a measuring method capable of measuring a phase delay characteristic between an input signal and an output signal of a measured device at high speed, with high accuracy and at low cost without influences of the noise, the spurious, etc.
In order to overcome the above subject, according to the present invention, there is provided a phase delay characteristic measuring apparatus for measuring a phase delay of a tested device based on phases of an input signal input into the tested device and an output signal output from the tested device, comprising:
an in-phase component calculating means for outputting a correlation value between input sampling data of the input signal and the output signal and ideal sine waveform data as a baseband I signal (in-phase component);
a quadrature component calculating means for outputting a correlation value between the input sampling data of the input signal and the output signal and ideal cosine waveform data as a baseband Q signal (quadrature component);
a phase angle calculating means for outputting phase angles of the input signal and the output signal based on the baseband I signal (in-phase component) and the baseband Q signal (quadrature component); and
a phase delay calculating means for calculating an amount of phase delay of the tested device from the phase angles of the input signal and the output signal.
According to this configuration, when the phase delay characteristic between the input signal and the output signal of the tested device is measured, the measuring apparatus that can execute the measurement at high speed with high accuracy at low cost without the influence of the noise, the spurious, etc. can be provided.
Also, in the in-phase component calculating means and the quadrature component calculating means, a calculation of
.a(n).b(n)
where a(n): input sampling data, and
b(n): ideal sine waveform data or ideal cosine waveform data
is executed by DSP.
Also, samplings of the input signal and the output signal are carried out over m periods (m=integer), respectively.
Also, a reference input signal and waveform data whose phase is shifted by 90 from the reference input signal by DSP are used in place of the ideal sine waveform data or the ideal cosine waveform data.
Also, the input signal and the output signal, which are to be sampled, are IF signals that are subjected to RF-IF conversion.
Also, a phase delay characteristic measuring method of measuring a phase delay of a tested device based on phases of an input signal input into the tested device and an output signal output from the tested device, comprising:
an in-phase component calculating step of outputting a correlation value between input sampling data of the input signal and the output signal and ideal sine waveform data as a baseband I signal (in-phase component);
a quadrature component calculating step of outputting a correlation value between the input sampling data of the input signal and the output signal and ideal cosine waveform data as a baseband Q signal (quadrature component);
a phase angle calculating step of outputting phase angles of the input signal and the output signal based on the baseband I signal (in-phase component) and the baseband Q signal (quadrature component); and
a phase delay calculating step of calculating an amount of phase delay of the tested device from the phase angles of the input signal and the output signal.
Also, in the in-phase component calculating step and the quadrature component calculating step, a calculation of
.a(n).b(n)
where a(n): input sampling data, and
b(n): ideal sine waveform data or ideal cosine waveform data
is executed by DSP.
Also, samplings of the input signal and the output signal are carried out over m periods (m=integer) respectively.